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[34.168.104.7]) by smtp.gmail.com with ESMTPSA id m190-20020a6258c7000000b005821c109cebsm7829231pfb.199.2023.01.12.15.29.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Jan 2023 15:29:56 -0800 (PST) Date: Thu, 12 Jan 2023 23:29:53 +0000 From: Sean Christopherson To: Matthew Rosato Message-ID: References: <20230112203844.41179-1-mjrosato@linux.ibm.com> <20230112140517.6db5b346.alex.williamson@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Intel-gfx] [PATCH v2] vfio: fix potential deadlock on vfio group lock X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: akrowiak@linux.ibm.com, jjherne@linux.ibm.com, farman@linux.ibm.com, imbrenda@linux.ibm.com, frankja@linux.ibm.com, pmorel@linux.ibm.com, david@redhat.com, linux-s390@vger.kernel.org, intel-gfx@lists.freedesktop.org, cohuck@redhat.com, linux-kernel@vger.kernel.org, pasic@linux.ibm.com, jgg@nvidia.com, kvm@vger.kernel.org, pbonzini@redhat.com, borntraeger@linux.ibm.com, intel-gvt-dev@lists.freedesktop.org Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Thu, Jan 12, 2023, Matthew Rosato wrote: > On 1/12/23 4:05 PM, Alex Williamson wrote: > > On Thu, 12 Jan 2023 15:38:44 -0500 > > Matthew Rosato wrote: > >> @@ -344,6 +345,35 @@ static bool vfio_assert_device_open(struct vfio_device *device) > >> return !WARN_ON_ONCE(!READ_ONCE(device->open_count)); > >> } > >> > >> +static bool vfio_kvm_get_kvm_safe(struct kvm *kvm) > >> +{ > >> + bool (*fn)(struct kvm *kvm); > >> + bool ret; > >> + > >> + fn = symbol_get(kvm_get_kvm_safe); > >> + if (WARN_ON(!fn)) In a related vein to Alex's comments about error handling, this should not WARN. WARNing during vfio_kvm_put_kvm() makes sense, but the "get" is somewhat blind. > >> + return false; > >> + > >> + ret = fn(kvm); > >> + > >> + symbol_put(kvm_get_kvm_safe); > >> + > >> + return ret; > >> +} > >> + > >> +static void vfio_kvm_put_kvm(struct kvm *kvm) > >> +{ > >> + void (*fn)(struct kvm *kvm); > >> + > >> + fn = symbol_get(kvm_put_kvm); > >> + if (WARN_ON(!fn)) > >> + return; > >> + > >> + fn(kvm); > >> + > >> + symbol_put(kvm_put_kvm); > >> +}